The development of the electron cyclotron maser (or gyrotron) has made possible the high efficiency generation of high power millimeter electromagnetic waves. The major drawback of gyrotron devices, however, is that they require a large magnetic field and a high energy electron beam. First harmonic generation of 1 millimeter waves in a gyrotron would require a magnetic field larger than 100,000 gauss. The physical size of the more conventional devices that do not require the use of large magnetic fields to produce high frequency radiation, such as the carcinotron, must be quite small to operate in the millimeter regime and this limits them to output powers of no greater than a few watts.
The orbitron maser concept, first proposed by Alexeff, has been demonstrated to produce high power millimeter and submillimeter electromagnetic radiation without the use of a magnetic field. However, Alexeff in U.S. Pat. Nos. 4,412,150 and 4,459,511 required voltage pulses in the range of 2000 volts and his theoretical description of the device assumed the orbits were circular about the center conductor. The present invention discloses the actual character of the electrons orbits have been shown to be noncircular and discloses a method requiring lower voltages. Alexeff's orbitron employs a coaxial cylindrical geometry with the inner conductor held at a positive electrostatic potential with respect to the outer conductor. Electrons are introduced into the interaction region by creating a glow discharge plasma between the inner and outer conductor and are electrostatically trapped axially so that they remain in the interaction region for a long period of time. The glow discharge, radial injection orbitron with axial trapping has several problems: low efficiency, poor mode control and inability to operate as a continuous wave. We have shown that these problems are obviated by using an axial electron injection and compression scheme similar to that used in most electron cyclotron maser devices. The disclosed method is termed AXIOM (Axial Injection Orbitron Maser).